To maintain the airway of an unconscious patient, and to achieve the objectives mentioned above, it is normal practice in general anaesthesia to use an endotracheal tube, which is a flexible tube of rubber or plastics, usually with an inflatable cuff around the distal end. Alternatively, an oro- or naso-pharyngeal airway may be used, which is a flexible tube extending from the mouth or nose into the pharynx but not into the larynx, and which is used in conjunction with a face mask, unlike the endotracheal tube. While preventing obstruction of the airway by the tongue, the oro- or naso-pharyngeal airway cannot conveniently be used for controlled ventilation and does not prevent inhalation of extraneous matter.
The endotracheal tube is introduced through the larynx into the trachea or windpipe, whereupon the cuff is inflated through a small auxiliary tube to seal against the wall of the trachea. Introduction of the endotracheal tube is a skilled operation normally requiring use of a laryngoscope to guide the tube through the larynx, past the vocal cords and into the trachea. There is a risk that the tube or the laryngoscope may cause damage to soft tissues or to the sensitive structure of the larynx. It is not alway possible to see the larynx, making intubation difficult or impossible in some patients. There can be a risk of accidental intubation of the oesophagus or of the right or left main bronchus. Placing of the tube in the trachea effectively narrows the interior passage or lumen of the trachea and provides a potential source of damage through infection or pressure while preventing normal upward flow of mucus from the trachea and rendering effective coughing impossible.
In my British Pat. Specification No. 2111394B, I have described and claimed an artificial airway device comprising a curved or flexible tube and a mask portion carried at one end of the tube, the mask portion having a flexible annular peripheral formation which may be inflatable and which surrounds a hollow interior space or lumen of the mask portion, said annular peripheral formation of the mask portion being pre-formed with a roughly elliptical shape such as to be capable of conforming to, and of fitting readily within, the actual and potential space behind the larynx so as to form a seal around the circumference of the laryngeal inlet without the device penetrating into the interior of the larynx, the tube opening into the lumen of the mask portion to provide the airway with the axis of the tube substantially aligned with the length of the roughly elliptical annular peripheral formation of the mask portion. The device thus constitutes a laryngeal mask. In practice, the annular peripheral formation has been made as an inflatable tube, e.g. of a silicone rubber.
This device has proved successful in use. Insertion of the device has been found to be easy and convenient in the majority of patients. A laryngoscope is not usually required. The mask does not enter the larynx or trachea so the risk of damage to these structures is avoided and the tracheal lumen is not narrowed as it is by insertion of an endotracheal tube. The risk of accidental entry into the oesophagus or one of the main bronchi is also avoided. Once in place the laryngeal mask generally permits the lungs to be ventilated by positive pressure. Alternatively the patient may be permitted to breathe spontaneously.
To avoid the risk that the epiglottis could obstruct the airway by falling inwards into the lumen of the mask and blocking the opening of the tube therein, which could happen, for example, with small displacements of the mask which may occur during surgery or manipulation of the patient on the operating table, I have described in my U.S. patent application No. 8713173 (Publication No. 2205499A) an artificial airway device of the kind described above wherein the airway tube opens into the lumen of the mask through an aperture which is provided with means, such as flexible cross-bars, to prevent it from being obstructed by the epiglottis while permitting passage of a second smaller tube, when required. Such a tube may be, for example, an endotracheal or endobronchial tube or a suction catheter, or an inspection tube such as a fibre-optic broncho- or laryngoscope.
The seal around the circumference of the laryngeal inlet which has been achieved, using an inflatable annular peripheral formation of the mask, has been found fully adequate in most circumstances. There are occasions, however, when an improved seal could be advantageous, e.g. to reduce the possibility that air might be allowed into the stomach when the patient's lungs are being ventilated under positive pressure, or to reduce the possibility that food regurgitated from the stomach might enter the lumen of the mask and the larynx. It is an object of one aspect of the invention to provide an improved seal around the circumference of the laryngeal inlet.